Particulate Filter for an Internal Combustion Engine

ABSTRACT

The invention relates to a particulate filter comprising a monolithic filter body ( 10 ) with inflow channels ( 12 ) and outflow channels ( 13 ) that run at an angle to said inflow channels. Each inflow channel is separated from the outflow channels by at least one filter wall. The inflow channels ( 12 ) run in a linear manner into a chamber ( 17 ), in which the ash collects. The purified gases exit the particulate filter via an outlet ( 21 ).

The invention refers to a particulate filter for an internal combustionengine, comprising a monolithic porous filter body with inflow channelsand outflow channels, each inflow channel crossing at least one outflowchannel from which it is separated by a filtering wall.

It is known to pass the exhaust gases of Diesel engines through a Dieselparticulate filter that retains the solid particles. The carbonparticulate matter that accumulates in the Diesel particulate filter isburned to ash in intervals. Such Diesel particulate filters have anoperating temperature on the order of 500° C. Ceramics and sinteredbodies are available for their manufacture. Conventional particulatefilters comprise a monolithic filter body of porous material includinglongitudinally extending channels. Alternately, these channels areclosed at the one end or the opposite other end. Two adjacent channelsrespectively form an inflow channel and an outflow channel. The filterflow passes through the wall separating both channels from each other.The manufacturing method, presently available only for ceramics, usesthe extrusion of a ceramic mass. Here, only profile structures of thechannels can be realized, wherein the inflow channels and the outflowchannels extend in parallel to each other. A respective channel isclosed at one end by a purposeful deformation of the channel wall.

This is due to the fact that greater temperature differences and thushigher thermal tensions occur with larger dimensions. This means that aDiesel particulate filter suited for a compact car cannot be transformedto a size suited for larger cars or even trucks simply by scaling it up.Finally, there is no easily maintainable and compact solution to theproblem of removing the ash resulting from the combustion process.

DE 30 43 996 A1 describes an airborne particles filter for Dieselengines, through which filter exhaust gases flow. The airborne particlesfilter is arranged in a tubular housing in an exhaust pipe behind theexhaust collection box. Within the housing, the airborne particlesfilter comprises a ceramic filter element in the form of a monolithhaving inflow channels and outflow channels. The inflow channels extendin parallel to each other on several parallel planes and the outflowchannels extend in the intermediate planes such that they cross theinflow channels. The monolith is mounted in the housing such that theoutflow channels are perpendicular and their upper ends are closed,whereas the lower end are in communication with the outlet pipe. Theinflow channels are open at both ends and receive, from opposite sides,the exhaust gases from the exhaust collecting boxes of the engine. Thecarbon particulate matter thus remains in the inflow channels.

It is an object of the invention to provide a particulate filter for aninternal combustion engine that is capable of cleaning voluminousexhaust flows charged with oxidizable particles.

The present particulate filter has the features of claim 1. Accordingthereto, the inflow channels open into a settling chamber which is anash chamber for depositing the ash.

In the present filter, the gas flow path passes through the porous wallbetween an inflow channel and a plurality of outflow channels, while theash remains in the inflow channel and can be removed therefrom eithercontinuously or in a separate cleaning process. At the outlet end of theinflow channels, a counter pressure is built up to cause the gases topass through the porous walls. The counter pressure is generated by thefact that the inflow channels open into a closed chamber. The ashchamber in which the ash is collected, may be chosen large enough to beable to accommodate all the ash accumulated during a filter's servicelife. Alternatively, the ash chamber may also have a cleaning openingthrough which ash can be removed.

The inflow and outflow channels crossing each other effect adistribution of the exhaust flow from each inflow channel to a pluralityof outflow channels. The inflow channels not only have open inlets, butalso open outlets. The particles contained therein can thus betransported to the outlet. The inflow channels are no one-way street forthe ash particles formed. Thus, it is possible to keep the poressubstantially free and to avoid or delay an obstruction of the filter.

While regeneration in conventional filters has the disadvantage thathighly excessive temperatures can occur in the end portion of thefilter, the invention avoids this effect. Because of the crossing flowpaths no thermal wave running through the filter is created.

Due to the crossing channels, the filter body cannot be made in amanufacturing method by extrusion or the like. The channel walls aremade of porous ceramics (SiC, Al₂O₃, . . . ) or metal sintered materialswhich catch the entrained solid particles as gases flow through andfilter them from the gases. The gas passing through the wall isdischarged from the monolithic solid body under an angle of >1° withrespect to the inflow channels. Crossing the inflow channels and theoutflow channels means that the flows are at a random angle to eachother that is different from zero.

The inflow channels and/or the outflow channels may have anycross-sectional shape, e.g. a round, triangular or quadrangular crosssection.

The complex monolithic filter body may be manufactured according tospecial manufacturing methods, e.g. in a Direct Typing Process, whereinlayers of pasty materials that have different patterns are layered uponeach other using a screen-printing machine.

In a preferred embodiment of the invention, the inflow channels aretubes passing through chambers without their walls contacting eachother, the chambers forming the outflow channels. Thus, it is achievedthat the entire circumferential surface of the inflow channels isavailable as a filter surface. In this manner, a relatively large filtersurface is realized in a volume.

The following is a detailed description of embodiments of the inventionwith reference to the drawings. This explanation is not be construed aslimiting the scope of the invention. Rather, the scope is determined bythe claims.

In the Figures:

FIG. 1 is a schematic illustration of a longitudinal section through afirst embodiment of the particulate filter,

FIG. 2 shows a section along line II-II in FIG. 1, and

FIG. 3 is a perspective schematic illustration of a second embodiment inwhich the inflow channels pass through chambers.

The particulate filter illustrated in FIGS. 1 and 2 is a Dieselparticulate filter for a Diesel engine. It comprises an integral porousfilter body 10 accommodated in a tube 111 and filling one half of thetube, for example. The filter body 10 is made of a porous material,especially of ceramics or sintered metal. It has a high thermalresistance of at least 1500° C.

Formed in the filter body 10 is a plurality of longitudinally extendinginflow channels 12 that are shown in light color in FIG. 2. In thiscase, the inflow channels are of rectangular cross section and aredefined by circumferential walls. One set of inflow channels 12 isrespectively disposed in a common plane. Located between two adjacentplanes of inflow channels 12 is a respective plane of outflow channels13. The inflow channels and the outflow channels are arranged such thatthey cross each other. In the present embodiment, they run at rightangles to each other. Filtering walls are situated between one set ofinflow channels 12 and an outflow channel 13. Of the four walls definingan inflow channel 12, only two walls act as filtering walls in thisembodiment, namely those walls that separate the inflow channel 12 fromthe adjacent outflow channels 13. The two other walls have no function.

The inflow channels 12 extend linearly through the filter body 10 froman inlet end 14 to an outlet end 15. In the tubular housing 11, theoutlet end 15 is followed by a pressure-tightly closed settling chamber17 which is an ash chamber. In the settling chamber, the flow velocityis reduced substantially and the ash is deposited. The inflow channels12 open into the chamber 17 in which a pressure builds up. The ash 18that has been formed in the inflow channels 12 and have reached thechamber 17 due to vibrations also accumulate there. The chamber 17 mayinclude a flap for removing the ash 18.

Above the filter body 10, a chamber 20 is provided in the housing 11,which extends along the entire length of the housing 11. The outflowchannels 13 of the filter body 10 open into this chamber 20. The chamber20 has an outlet opening 21 through which the cleaned gases escape.

In operation as a Diesel particulate filter, the vehicle exhaust gasesthat are indicated by the arrows 23 are fed to the inflow channels 12.The carbon particulate matter settles in the filter body 10, whereas thegases flow through the filtering walls into the outflow channels 13 andfrom there into the chamber 20.

To regenerate the filter body 10, the same is heated so that the carbonparticulate matter oxidizes and burns to ash. Thereby, the pores of thefiltering walls are cleared again. Vehicle vibrations and the effect ofthe gas flow transport the ash into the chamber 17.

Whereas in the first embodiment only two of the four walls of eachinflow channel 12 act as filtering walls, all four walls of theembodiment in FIG. 3 are filtering walls. In this embodiment, the inflowchannels 12 extend as rectangular tubes from an inlet end 14 to anoutlet end 15. The outlet end 15 leads to a closed chamber (notillustrated) which may be configured as an ash chamber.

Along the length of the inflow channels 12, the filter body is dividedinto chambers 28, 29 by transverse walls 25, 26 and 27, which chambersform the outflow channels 13. the cleaned gases 30 leave the filter bodyand reach a collecting chamber (not illustrated).

It can be seen in FIG. 3 that each inflow channel has four filteringwalls W1, W2, W3 and W4. This is possible because the tubular inflowchannels 12 are spaced apart from each other. The walls 25, 26 and 27also serve to mechanically hold the inflow channels 12.

The function of the Diesel particulate filter of FIG. 3 is the same asthat of the first embodiment so that the description thereof will not berepeated.

1. A particulate for an internal combustion engine, comprising a monolithic porous filter body having inflow channels and outflow channels, each inflow channel crossing at lest one outflow channel from which it is separated by a filtering wall, wherein the inflow channels open into a setting chamber which is an ash chamber for depositing ash.
 2. The particulate filter of claim 1, wherein each inflow channel crosses a plurality of outflow channels and each outflow channel crosses a plurality of inflow channels.
 3. The particulate filter of claim 1, wherein a plurality of inflow channels are arranged adjoining in a first plane and a plurality of outflow channels are arranged adjoining in a second plane parallel to the first plane.
 4. The particulate filter of claim 1, wherein the inflow channels are tubes that pass through chambers without their walls contacting each other, said chambers forming the outflow channels.
 5. The particulate filter of claim 1, wherein the outflow channels are tubes that pass through chambers without their walls contacting each other, said chambers forming the inflow channels.
 6. The particulate filter of claim 1, wherein the settling chamber has a flap for removing the ash therefrom. 